Another balun question... this one for HF

For HF work, I recently bought an end-fed 6m - 40m multiband antenna from Honolulu EARC (Emergency Amateur Radio Club - Hawaii) which features a 9:1 UNUN at the end of a 30' vertically-mounted longwire. In addition to (somewhat) matching the high impedence of the antenna, will it also serve double duty to prevent RF from coming back into the shack from the antenna, like the 1:1 balun?



I understand that I'll have to use an outboard antenna matcher for this antenna, the Yaesu 857D's internal antenna matcher is not likely to be able to match it very effectively. Thanks!